In association with the recent increase in communication traffic, necessity of expanding the transmission capacity of communications has been increasing. In particular, it is expected that the transmission capacity is expanded by the use of an optical communication network system using light. In such an optical communication network system, a module for performing transmission and reception of optical signals is a key device. Such a module for optical communication is required to have a higher speed and a smaller size, in association with increase in the system's speed and capacity.
In general, a light-receiving module for optical communication is composed of the following components. That is, the components include an optical fiber for transmitting optical signals, a PD (Photo Diode) for performing optical-electrical conversion of optical signals sent from a transmission line, a TIA (Trans Impedance Amplifier) for performing impedance conversion and amplification of the current signals thereof and then outputting the signals in the form of voltage signals, and the like. These components are mounted on a ceramic package or the like, thereby being modularized together. In the modularization, it is important to hermetically seal the components within the package, in terms of securing the reliability of the optical communication module.
Also at a portion for introducing an optical fiber into the package, various hermetic sealing schemes are employed, so as to secure the reliability of the optical communication module. Patent Literature 1 (PTL1) describes an example of such modularization into a package for optical communication, with optical fibers mounted there.
A method of plating the inner surface of a cylindrical member described in Patent Literature 1 (PTL1) is defined to be one which partially plates the inner surface of a cylindrical member (introduction pipe) provided in a package for optical communication. More specifically, it is described that the inner surface of the introduction pipe is partially masked at its portion not to be plated, and in that state, the exposed portion of the inner surface of the introduction pipe is plated. It is then described that the method has an effect that, when fixing an optical fiber to the introduction pipe using molten solder, the molten solder does not penetrate into the package. It is then described that, due to the effect, it becomes possible to prevent either degradation of the sealing quality caused by decrease in the solder amount at the sealing portion of the introduction pipe or degradation of the reliability caused by solder having penetrated into the package.
Patent Literature 2 (PTL2) describes an optical fiber assembly and a sleeve used for the assembly, which are, respectively, an optical fiber assembly for connecting an optical fiber to an optical communication module, and a sleeve attached to an optical fiber cable. It is described that an insertion hole is provided in a housing corresponding to a package for optical communication, the optical fiber assembly is inserted there, and the housing and the sleeve are fixed together by soldering. Patent Literature 3 (PTL3) proposes to join an insulating substrate with a base board by soldering.
More recently, for the purpose of increasing the speed and capacity of optical communications, multi-channelling is increasingly conducted, where a large number of communication channels are set. For example, a configuration provided with four channels each having 10 Gbps capacity or the like has been developed to realize 40 Gbps capacity. In association with such a technology trend of multi-channeling, research and development on multi-channeling also in the inside of an optical communication module has been conducted. Examples of such research and development include that on a configuration where optical fibers for transmitting optical signals are multi-channeled and then an optical fiber array with the optical fibers aligned is used, that on a configuration where the optical fiber array is mounted inside a package, and the like.